Method of making selenium elements



Oct. 3, 1944. A. J. MILLER ET AL 2,359,377

METHOD OF MAKING SELENIUM ELEMENTS Filed Nov. 25, 1942 @9 1 v l,g ,7 11mum INVENTOR. 'HRTHUR .J. MILLER EUGf/VE R SAUL-RBORN Patented Oct. 3, 1944 2,359,377 METHOD OF MAKING SELENIUM ELEMENTS Arthur J. Miller and Eugene P. Sauerborn, Newark, N. J., assignors to Federal Telephone & Radio Corporation, New York, N. Y., a corporation of Delaware Application November 25, 1942, Serial No. 486,858

s'claims.

This invention relates to selenium coated ele ments and to a method of making and treating them; and it has for its object to provide a convenient method for rapidly making and processing a large number of such elements.

Selenium coated elements such as are ordinarily used for rectiflers or photocells ordinarily comprise a base or carrier disk or plate such as iron or steel or aluminum which may be coated with another substance such as nickel. A layer 01' selenium is spread over the surface of such a base plate, for example by fusing or condensing selenium vapor thereon or compressing a layer of selenium powder at elevated temperatures. Such a coated base plate is then ordinarily treated further by heat to produce the proper crystal structure in the selenium, and given further treatments to adapt it as a rectifier or a photocell. For example, a counter electrode is applied over the surface of the selenium as by spraying with a conducting substance such as Wood's metal, and it may then be given an electro-forming treatment by the application of voltage between the base and counter-electrode.

It is desirable to be able to carry out the steps in the fabrication and treatment of the elements on a large number of the elements at one time. This is done in accordance with the present invention by providing a webbing of selenium to bind a large nunmber oi the base plates or disks together, so that they can be handled as a unit in the treatment.

The invention will be more fully understood from the following detailed description taken in conjunction with the drawing of which:

Fig. 1 is a top view of a disk used as a support for a selenium coating, and Fig. 2 is a side view of the disk;

Fig. 3 shows a large number of the disks oi Fig. 1 placed side-by-side on a plate;

Fig. 4 is a side view of the arrangement shown in Fig. 3;

Fig, 5 shows a selenium powder spread over the arrangement of Figs. 3 and 4; and

Fig. 6 shows the disks of Fig. 5 held together by a webbing of selenium.

Figs. 1 and 2 show a circular disk I which may be iron or steel or aluminum and may be nickel plated, if desired, to be used as a carrier or base plate for a coating of selenium. These disks may be of a small size such as a 10 mm. diameter, in which case they will ordinarily have no hole in the center. Or on the other hand, they may be of a larger diameter and have the usual central mounting pole indicated by the dotted line 2 in Fig. 1. These disks are then laid side by side on a flat plate 3 (Figs. 3 and 4) so that the adjacent disks are close together but do not quite toucheach other. The selenium is then sprinkled in asflne powdery form over the plate 3 and disks l lying thereon until a layer of suitable thickness covers all the disks; for example a thickness of around .02 inch as indicated by the powder line 4 of Fig. 5. The powder will then evenly cover all the disks and also the spaces on plate 3 between them. The powder might be applied to a thickness either less than, or equal to, or even somewhat greater than, the thickness of the disks.

The powder-covered assembly of Fig. 5 is then inserted in a press at an elevated temperature.

The press temperature should preferably be around 0. although it may vary considerably on either side 01' this value; but the temperature should not be so high as to reach the melting point of the selenium. The pressure should be quite high although it is not critical. A pressure of about 5000 pounds per square inch is satisfactory although it may vary considerably from this. The selenium powder is compressed on the disks in this manner for a short time, for example, one or two minutes, which will be suflicient at the temperature and pressure suggested to mold the powder to the disks with a firm adherence, and the excess selenium between the disks will be formed as a web'oi which the individual particles of selenium are fairly rigidly welded together. I! the thickness of the powder applied was less than the thickness of the disks, there will usually be no pressure applied at the web areas except immediately around the disks where it has been extruded oil? the disks. If the thickness of the powder was greater than that of the disks the web areas will undergo pressure as well as heat. In either case the web formation is vsuillciently strong. The webbing, whilefragile relative to the disks, is strong enough so that all the coated disks l on plate 3 may be removed from the plate as a unit held together by the webbing as shown in Fig. 6.

This unitary structure is useful for simultaneously treating all of the coated disks in such ways as is desired. For example, the next step in a heat treatment can be easily undertaken by putting the unit in an oven and giving it the usual heat treatment at around 200 C. for some time to develop the crystal formation of the selenium. The unit may then be taken out and given further desired treatment such as fuming with selenium dioxide or lacquer treatments. The usual counter electrodes may then be applied by placing over the coated disks a mask with holes properly spaced to leave uncovered the desired portions of the disk: and a suitable metallic spray such as Wood's metal may be sprayed on to form the well known counterelectrode. Then if desired the elements may be all electro-formed together by the application of a voltage between the counterelectrodes and the base plates to induce the formation of blocking layers to improve the rectifier characteristics.

The individual coated elements may be separated from each other merely by breaking away the fairly fragile webbing between them.

It will be understood that any one or all of the foregoing treatments may be given the elements and the process of joining the individual elements together by a webbing can be used with any method. The method is not necessarily limited to use with circular disks as the disks might be of any desired shape.

What is claimed is:

1. The method of fabricating a plurality of selenium elements as a unit which comprises placing a plurality of base plates on a supporting plate, sprinkling selenium powder over the base plates and in the spaces therebetween, compressing the powder against the base plates at an elevated temperature to mold the powder to the base plates and form a frangible webbing between them, and removing said supporting plate, whereby said base plates remain held together by said frangible webbing.

2. The method of fabricating a plurality of selenium elements as a unit which comprises placing a plurality of base plates on a supporting plate, sprinkling selenium powder over the base plates and in the spaces therebetween, compressing the powder on the base plates against the base plates, while at the same time compressing the powder which is between the base plates against the supporting plate, at an elevated temperature below the melting point of selenium so as to mold the powder to the base plates and to form a frangible webbing between them, and removing said supporting plate, whereby said base plates remain held together by said frangible webbing.

assasvv 3. The method of fabricating a plurality of selenium elements as a unit which comprises placing a plurality of base plates on a supporting plate, sprinkling selenium powder over the base plates and in the spaces'therebetween, the powder in the spaces therebetween being sprinkled to a thickness no greater than about the thickness of the base plates, compressing the powder against the base plates at an elevated temperature below the melting point of selenium to mold the powder to the base plates under pressure and to form an adherent frangible webbing between them without pressure. and removing said supporting plate, whereby said base plates remain held together by said frangible webbing.

4. The method of treating a plurality of selenium elements in unison which comprises placing a plurality of base plates on a supporting plate, sprinkling selenium powder over the base plates and in the spaces therebetween on said supporting plate, compressing the powder against the base plates at a high temperature below the melting point of frangible selenium to form a selenium webbing between the base plates suillciently strong to hold the base plates together, and removing said supporting plate, whereby said base plates remain held together by said frangible webbing.

5. The method of treating a plurality of selenium elements as a unit which comprises placing a plurality of base plates on a supporting plate,

spraying selenium powder over the base plates and in the spaces therebetween on said supporting plate, compressing the powder against the base plates at an elevated temperature below the melting point of selenium to mold the powder to the base plates and to form a thin frangible webbing therebetween and removing said supporting plate, whereby said base plates remain held together, by said frangible webbing, then heat treating the web-Joined base plates, and then applying a counter electrode to the selenium surfaces.

ARTHUR J. MILLER. EUGENE P. BAUERBORN. 

